1. Field of the Invention
The present invention relates to a design rule generation and, in particular, a system for automatically generating a design rule and a recording medium recording a program thereof.
2. Description of the Background Art
In recent years, to comply with the high integration and miniaturization of semiconductor integrated circuits, there proceeds rapidly the miniaturization of resist patterns formed on wafers and that of mask patterns for forming the resist patterns. In photolithography technique, super resolution technique is used as one method other than shortening the wavelength of light source, for improving resolution such as to comply with the miniaturization. Examples of the super resolution technique are so-called Levenson method and modified illumination method.
In the Levenson method, by disposing a phase shifter on a mask, the resolution of a resist pattern formed on a wafer is increased to comply with the miniaturization. In the modified illumination method, by changing the shape of a light source itself, the resolution of a pattern formed on a wafer is increased to comply with the miniaturization. With these super resolution techniques, a further fine resist pattern can be formed, but there is the possibility of causing a different dimensional change than has hitherto been caused.
Specifically, in a method employing no super resolution technique, any layouts in which line width and space width are below resolution limit are prohibited, and a mask pattern is laid out such that line width and space width are not less than the resolution limit. Thereby, no large dimensional change occurs between the mask pattern and the pattern formed on a resist (finished pattern), and the dimensional change in the finished pattern falls within a predictable range. When employing a super resolution technique, line width and space width that are resolution limits can be reduced. In a certain dimensional range, however, the finished pattern size is far thick or thinner than a mask pattern, resulting in beyond a permitted limit in some cases. Further, it may on occasion be difficult to predict this. As a technique for solving this problem, optical simulation has been used in recent years.
Optical simulation is a technique for predicting the shape of a finished pattern. This enables to make a design rule (referred to simply as a xe2x80x9cDRxe2x80x9d in some instances) corresponding to a super resolution technique, based on the predicted shape of the finished pattern.
Now, a schematic flow chart of a semiconductor device manufacture is given in FIG. 23. In the manufacture of a semiconductor device, as shown in FIG. 23, a circuit design and its verification are performed (step S101) and, based on the designed circuit data, a layout design and its verification for determining an actual circuit pattern formed on a wafer are performed (step S102). Then, based on the layout design, a wafer process is executed (step S103). The design rule is used for the layout design and verification shown in step S102. That is, it is the rule for specifying, for example, the line width of wiring and the space width of wirings, and is restricted by wafer process.
In photolithography being one wafer process, when no super resolution technique is employed, a design rule of the same layer is relatively simple. Specifically, all required therefor is to specify a minimum line width (L) and minimum space width (S) which show the wafer process limit (e.g., a resolution limit in photolithography).
On the other hand, when a super resolution technique is employed in a wafer process, a complicated design rule is required to comply with the super resolution technique. For example, in forming a wiring pattern having various space widths S, as shown in FIG. 24, it is insufficient only by specifying a minimum line width L and minimum space width S, and thus required to determine whether resolution is executable or not in a combination of a line width and space width, namely, whether the finished pattern size exceeds a permitted limit or not.
Then, for satisfying this requirement, a method of making a matrix table as shown in FIG. 25, has been taken. FIG. 25 shows a so-called L/S matrix that is a table in which various numerical values of line width and space width of a wiring pattern are disposed vertically and laterally, respectively, in order to make understandable a plurality of combinations of line width and space width.
Referring to FIG. 25, disposed vertically are the numerical values of line width L (unit: xcexcm). These are disposed at intervals of 0.02 xcexcm in the range from 0.14 xcexcm to 0.4 xcexcm, at intervals of 0.1 xcexcm in the range from 0.4 xcexcm to 1.2 xcexcm, and the last numerical value is 1.5 xcexcm or more. Disposed laterally are the numerical values of space width S. These are disposed at intervals of 0.02 xcexcm in the range from 0.14 xcexcm to 0.4 xcexcm, at intervals of 0.1 xcexcm in the range from 0.4 xcexcm to 1.2 xcexcm, and the last numerical value is 1.5 xcexcm or more. In this table, for instance, region A covers the line width L of 0.30 xcexcm to 0.32 xcexcm, and the space width of 0.24 xcexcm to 0.26 xcexcm.
Referring now to FIGS. 26 and 27, a method of using a L/S matrix is described. FIGS. 26 and 27 express the L/S matrix of FIG. 25, for general purpose. Although no specific values of line width L and space width S are indicated, it is set such that line width L increases as it moves downward in the vertical direction, and space width S increases as it moves rightward in the lateral direction.
FIG. 26 is a table illustrating the resolvability based on the calculation result obtained by optical simulation, when no super resolution technique is employed. Region A1 of the hatched part corresponds to the region covering combinations of line width and space width, with which an optical image of a pattern defined by lines and spaces is resolvable on an image surface of an optical system in photolithography, e.g., on a resist.
The region A1 is of a simple rectangle. Thus, it will be apparent that the region A1 can be specified as a design rule, merely by specifying the minimum line width and minimum space width which show a resolution limit in photolithography.
On the other hand, FIG. 27 is a table illustrating the resolvability based on the calculation result obtained by optical simulation, when the modified illumination method is employed as a super resolution technique. Regions A1 and A2 of the hatched part correspond to the region covering combinations of line width and space width, with which an optical image of a pattern defined by lines and spaces is resolvable on a resist. The region A2 is such a region that surrounds the corner of the region A1, and is a peculiar result when used an aperture for annular illumination in the modified illumination method. It will be apparent that the shape of the resolvable region is complicated by the presence of the region A2, thus requiring a complicated rule for specifying that region as a design rule.
As described in the foregoing, when the super resolution technique is employed in a wafer process in order to comply with the high integration and miniaturization of semiconductor integrated circuits, a complicated design rule is required for complying with the super resolution technique. Hitherto, the design rule has been obtained by the following manner. That is, the designer sequentially makes an optical simulation to various combinations of line width L and space width S, to make a L/S matrix, and determines whether resolution is executable or not, in the respective combinations of line width and space width, by using the L/S matrix. Based on the results, a design rule is determined empirically. Thus, the efficiency of operation to determine a design rule is poor, and a long time is required to determine the design rule. Further, it is impossible to make determination for all the combinations, and thus limited to checking of every important point.
According to a first aspect of the present invention, a design rule generation system comprises: (a) an automatic wiring pattern generation part that automatically generates a wiring pattern comprised of a combination of a wiring width and a space width between the wirings; (b) an optical simulation part that performs an optical simulation under a condition of printing the wiring pattern on an object, and outputs data of an exposed light on the object; (c) a finish prediction part that predicts a finished size of the wiring pattern to be formed on the object, based on the data of the exposed light; (d) a matrix database construction part that records, on a data table in the form of a matrix, resolvability of a plurality of the wiring patterns having different combination of the wiring width and the space width which are obtained by repeating the respective operations in the parts (a) to (c); judges whether the finished size satisfies a predetermined condition or not, so that it is determined the wiring patterns are resolvable if the predetermined condition is satisfied, and determined the wiring patterns are unresolvable unless the predetermined condition is satisfied; and records the resolvability of the wiring pattern on the data table, so as to correspond respectively to the combinations of the wiring width and the space width; and (e) a design rule generation part that generates a design rule by defining a range of a resolvable region comprised of a set of the wiring patterns being resolvable, or an unresolvable region comprised of a set of the wiring patterns being unresolvable, based on the data table.
According to a second aspect, the design rule generation system of the first aspect is characterized in that the data of the exposed light outputted from the optical simulation part is data showing a light intensity distribution corresponding to a position on the object; the finish prediction part sets a predetermined light intensity in the light intensity distribution, as a threshold value, and employs a section width obtained by slicing the light intensity distribution with the threshold value, as the finished size; and the matrix database construction part determines resolvability of the wiring pattern by determining whether the section width is contained in a size obtained by summing the wiring width, the space width and a predefined allowed variational value.
According to a third aspect, the design rule generation system of the first aspect is characterized in that the matrix database construction part contains at least an exposure margin and defocus margin, as a criterion of determining resolvability of the wiring pattern.
According to a fourth aspect, the design rule generation system of the third aspect is characterized in that the data of the exposed light outputted from the optical simulation part is data showing a light intensity distribution corresponding to a position of the object; the finish prediction part sets a plurality of light intensity values in the light intensity distribution as a plurality of threshold values, respectively, and acquires a plurality of section widths by slicing the light intensity distribution with the threshold values; and the matrix database construction part determines resolvability of the wiring pattern by finding, out of the section widths, ones which fall within a range of a dimension obtained by summing the wiring width, the space width and a predefined allowed variational value, finding an allowed variational exposure energy from a range of threshold values corresponding to the section widths, and determining whether the allowed variational exposure energy is contained in the exposure margin.
According to a fifth aspect, the design rule generation system of the third aspect is characterized in that the optical simulation part performs the optical simulation under a plurality of defocus conditions, to output data showing a plurality of light intensity distributions which correspond to the defocus conditions, respectively, and correspond to a position on the object; the finish prediction part sets a predetermined light intensity in the light intensity distributions, as a threshold value, and acquires a plurality of section widths by slicing the light intensity distributions with the threshold value; the matrix database construction part determines resolvability of the wiring pattern by finding, out of the section widths, ones which fall within a range of a size obtained by summing the wiring width, the space width and a predefined allowed variational value, finding an allowed variational defocus amount from a range of defocus conditions corresponding to the section widths, and determining whether the allowed variational defocus amount is contained in the defocus margin.
According to a sixth aspect, the design rule generation system of the first aspect is characterized in that the automatic wiring pattern generation part generates a wiring pattern of oblique lines in which the wiring and the space are disposed obliquely on a plain at a predetermined angle.
According to a seventh aspect, the design rule generation system of the first aspect is characterized in that the automatic wiring pattern generation part generates a hole pattern in which the wiring width and the space width are employed as the diameter of holes and the space width between the holes, respectively.
According to an eighth aspect, the design rule generation system of the third aspect is characterized in that the matrix database construction part contains the presence/absence of a dimple occurred in the space between holes, as a criterion of determining resolvability of the wiring pattern.
According to a ninth aspect, a recording medium records a program for realizing on a computer the following functions: (a) an automatic wiring pattern generation function of automatically generating a wiring pattern comprised of a combination of a wiring width and a space width between the wirings; (b) an optical simulation function of performing an optical simulation under a condition of printing the wiring patter on an object, and outputting data related to an exposed light on the object; (c) a finish prediction function of predicting a finished size of the wiring pattern to be formed on the object, based on the data of the exposed light; (d) a matrix database construction function of recording, on a data table in the form of a matrix, resolvability of a plurality of the wiring patterns having different combination of the wiring width and the space width to be obtained by executing repetitively the functions (a) to (c); judging whether the finished size satisfies a predetermined condition or not, so that it is determined the wiring patterns are resolvable if the predetermined condition is satisfied, and determined the wiring patterns are unresolvable unless the predetermined condition is satisfied; and recording the resolvability of the wiring patterns on the data table, so as to correspond respectively to the combinations of the wiring width and the space width; and (e) a design rule generation function of generating a design rule by defining a range of a resolvable region comprised of a set of the wiring patterns being resolvable, or an unresolvable region comprised of a set of the wiring patterns being unresolvable, based on the data table.
The design rule generation system of the first aspect offers the following advantage. Specifically, in a conventional manner to obtain a design rule, the designer sequentially makes an optical simulation to various combinations of line width and space width, to make a L/S matrix, and then determines whether resolution is executable or not in the respective combinations of line width and space width, by using the L/S matrix. Based on the results, a design rule is determined empirically. On the other hand, with the design rule generation system of the first aspect, a L/S matrix in the form of a matrix can be automatically generated and a design rule can be automatically determined. This increases the efficiency of operation for determining the design rule, and reduces the time needed in determining the design rule.
With the design rule generation system of the second aspect, a finished size can be obtained at high precision, for example, by previously making certain of the association between the exposure energy and threshold value, with measurements and optical simulations, and employing, as a finished size, a section width which is obtained by slicing a light intensity distribution with a threshold value corresponding to the real exposure energy.
With the design rule generation system of the third aspect, a design rule suited for the real wafer process in which exposure energy might change and defocus might occur, can be obtained because at least one of an exposure margin and defocus margin is contained as a criterion of determining the resolvability of a wiring pattern, in the matrix database construction part.
The design rule generation system of the fourth aspect enables to obtain a specific method of considering an exposure margin, and a design rule suited for the real wafer process involving the variation in exposure energy.
The design rule generation system of the fifth aspect enables to obtain a specific method of considering a defocus margin, and a design rule suited for the real wafer process involving the variation in defocus amount.
The design rule generation system of the sixth aspect, a design rule of a wiring pattern of oblique lines can be obtained by generating a wiring pattern of oblique lines in which wirings and spaces are disposed obliquely on a plain at a predetermined angle, in the automatic wiring pattern generation part.
With the design rule generation system of the seventh aspect, a design rule of a hole pattern can be obtained by generating, in the automatic wiring pattern generation part, a hole pattern in which the wiring width and space width are taken as the diameter of holes and the space width between holes, respectively.
With the design rule generation system of the eighth aspect, a design rule taking the presence/absence of a dimple into consideration can be obtained because the presence/absence of a dimple occurred in space between holes is contained as a criterion of determining the resolvability of a wiring pattern, in the matrix database construction part.
With the recording medium of the ninth aspect, a data table in the form of a matrix can be automatically made by executing, on a computer, the program recorded in the recording medium, and a design rule can be determined automatically. This increases the efficiency of operation for determining the design rule, and reduces the time needed in determining the design rule.
In view of solving the foregoing problems, an object of the invention is to provide a system in which a design rule determination process is automated to increase the efficiency of operation for determining a design rule, thus requiring lesser time needed in determining the design rule.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.